Froth flotation apparatus



July 20, 1954 P. M. PAYNE FROTH FLOTATION APPARATus 4 Sheets-Sheet lFiled Dec. 7, 1951 [W23 I na lJlp. 'a W wm P M. N R

A E P/ (Ittomeg July 20, 1954 P, M, PAYNE 2,684,233

FROTH FLOTATION APPARATUS Filed Dec. 7, 1951 4 Sheets-Sheet 2 L [7mm 23i l 24/ F ig. 2 '5 lo :Srwentor F'g' 3 PEARsoN M. PA N (Ittomeg July 20,1954 Filed Dec. '7. 1951 P. ML PAYNE 2,684,233 FROTH FLoTATIoN APPARATUS4 Sheets-Sheet 3 3nventor PEARSON M. PAYN (Ittorneg July 20, 1954 PM.PAYNE 2,684,233

FRoTH FLoTATIoN APPARATUS Filed Dec. '7l 1951 4 Sheets-Sheet 4 JnventorPEARSON M PAYNE Gttorneg .cienc' andxfacilitate Patented July 20, 1954'U N21 TED 'S LS PATENT z-fO'F'FalC'E i` FROTHHYFLO TATIONI ;APPATSPearson. M.` Payne, Denver, `C'oio.

Application `December 7, 1951, Serial' fNo.'.26 0,480

(Cl. I?61--- 93) `llClairris. .1

This invention relates togapparatus iorthe agtationa'nd iroth fiotativeseparation of granu'lar -or'comminnted materials, such-as ores, and;more particuiarly .tog-agitating and. froth ;fiotation-.apparatus ofthe generaltype vand operativezorgan- .iza-tion disolosecl in myapplication .for Letters Patent oitheUnited 'Statesfiled .on August1l3,19.48,' serialrlo. 44,118, Vnow issuecl .under .dateof December ,11,1951, as v;Patent No.2,577,8)2, :and has asan ohjecttoprovide novelandimproved means; in. combination-. and operative association with theapparatus zofz my .said earlier patent effective to extencl.the-Utility, .enhanoe thezeffi- -regulation and .operative controlthereof.

lviy eariierxpatent above identifie-(iiscloses the :operativezassociation with. a flotationeh .or .agitatihg ;compartmentfofiagitatingand -air incluc- -tion`` means. inlthe ;formV of a vvertical-ly-axiseoLrotatable "iinpeller :unit characterized by. xedlyassociated,angularly-spaced, ;like ;rods or :stiii ,whip elements ;diverging;outwardly v.ar-1d:olown- :fvvardiyin ;intersecting relationwith thelevel of the materia to ibeiagitated and `through 'thelbocly of such;materialzto terminationin.free ends spacedly adiacent ;the fioorfof thecell; or .compartment, vand ;the improvements-of "theinstant inventionrelate .to -means Tor; efiectively; applyiinfcfA the agitationszand: airinductions incident to rotation of such an fimpeller to efiicient-nsein,the conditioning. of materials Iintrorluced within vthe .cell or.Vcompartrnent, .to the seleetive iroth fiotati-ve. .separ-aticnl of such`materials, .to the recirculatonlof -the cell or cornpartmentV contentstoand through the `influenoe of l,theimpellen andto the .regulationandAcontrol of suchoperations.

,Withuthe foregoing andv other objects in view, my inventionconsists inthe. construction,` arrangement, andcombination of elements ashereinafter, setiorth, pointed out ,in myclaims, and illustrated by the.accornpanying .drawings, in whch- .Figure 1 sideelevationpartly inVertical section, ofV`` a laboratory batch fiotation machine embodyingthe`l disclosuresA ofmy, earlier application ,as V typically associated.i With the. improvements hereinafter'descrihecl. 'Figurez' is aVertical section, on a relatively enIaITgBd Scale, taken axi'allythrough .the cell and impeller organization of the apparatnsshownirrFigure 1. ,Figura 3 is a cross section. taken substantally on theindicated line 3-;3 of Figure 2. 'lfigure 4 is a cross section' takenlsubstantiallyon the indicated line 4-4 of Figura, 2. Fg'ure 5 isa'fragmentary, de- .taill Vertical section, on afurther eniarged Scaleand withportionsfbroenawayto conserve space, taken"suhstantiallyf;axially-Vf .altitudinallyarijustable-mounting-,andsupport utilized. in the organizatienaccording tofFigure 1. Figure .6is-a dettl crQss.section,--on a vrelativelyenlargecl scale,taken-substantia-lly ,'Qn; heindieatecl linel 6-6 'of Eigure 1.Figure'lis atop plan. view ofan alternative embodimentand adaptation ofthe invention. Figurefisamertical section takensubstantially ontheindicated-linesB-TS of Figure'Y. Figure 9 isza ficross'.section,.on, arelativelyfien- ;largedscale, `taken-snlostant'lallyI on vthe indicatedline9-S of fFig1 ire 8. Figure 10 isa fragmentary, detail; sectiontakensubtantiaHy on the indicatediine ,It- .-l' of EigureQ.

vIn the. embodimentzof the invention typified by Figuresl-, inchisve,vof, the'olrawingsa froth fiotation `.cell is conventionally, representedJas a relatively-;ieep, conveniently-cylindriaL opentoppbowl .iii iormdwitha `froth-overfiow lip H cooperatingwith a l.ntch intheupper marginofthe bowl.-.wall. :The-bowl .1.0 is shown. as carried by and toupstandr,withj-itsiaxis Vertical from-,a base; i-whichsnpportsashereinafter more particularly described, an .altitudinally-adjustabledriveandzop-erative cmounting' forl animpeller shaft-i3 coax ial.with.said boWl-and .rotatable `aboutits axisin an'operative dispositionintersecting thevplane of`1 the bowl top rim. Fixed ,-t0 .androtatablewith the-lower end of the shaft 1,3,

van .impeller assembly, 4comprising a plurality of like, stiif, rodelements' l 4. fixedlyengagedat-thir .upperends .imandzwith a-collar ,I5. secured to Vthe shaft. 13 anclfcorrepondingly `clivergingoutwardlyand ,downwarlyrromz ,said .collar inaoniform .angular spacingciefinitye of a hollow frustumof a `cene-is mounted `and disposed forrotation within the bowlglfl with the divergent free lower enclsof thevrods |.4.we11.spaced,from and ,to clear .the bowl bottomrandr-sidezwallareasl andthe'collar -I-labove the,normalg.pulp.1evel ofthebowl 'todispose said rods in norrnaiintersectingrelation with the=-surf;aceofthe:,bowl-'charge as indicated atL in Figure 2. Tofoprativelymount and,adjustablyfsupport; Lthe; shat l 3 v: and its .associatedimpellerassemhly, na;postf i fixelly Aupstancling fromthe base.` ,ILinaxial parallelism withA and` at one .side ,'-otthe `boizvlf I 0.slidaloly.` .engages within and `reciprooablyftfincmntsl a tubular.memberil'l fixedly .related at its upper end with arightangulararmflBarranged to overhang the bowl'l andv a'sleevel9=on"the -free end of saidarm'i-is -arranged torotatably accommodateand to be traversed by' ,thefshaft 13' ina coaxial relationship ofsaidsleeve, 'shaft,, and the bowl li). A bracket 2i adjustably engagedwith the member ll upper end in an extension laterally therefromopposite to the arm iii projection mounts an electric motor :ii with itsshaft paralleling the shaft i3 so that coplanar pulleys 22 and 23 xedrespectively to the motor shaft upper end and to the end of the shaft E3above the sleeve 19 and interlinked by a belt 2d may function as a drivefor the shaft SS and its impeller assembly powered by said motor 25.Selective altitudinal adjustment of the member il and the elementscarried thereby is provided through the agency of a rack 25 fixedlongitudinally of the post Hi interiorly of said member, a gear 2%rotatable in ears 21 outstanding in spaced parallelism from said memberand meshing with the rack 25 through an opening in the member wall, ahandle 28 for the manual rotation of the gear 26, and a ratchet anddetent arrangement 255 effective to hold the gear 25 in any adjustedrelationship along the rack 25, the adjusting means shown and describedbeing capable of functioning in an obvious manner to elevate and lowerthe impeller assembly axially of the bowl iii and to hold said assemblyavailable and in condition for operation at any position in its range ofaltitudinal adjustment.

All of the foregoin'g is but typical of organizations and arrangementsutilizing the novel impeller asseinbly and operative relationshipsdisclosed in inv earlier Patent No. 2,577,802, and is herein illustratedand described as representative of known means and particularcombinations -wherewith and wherein my further improvements are ofespecial advantage, it being readily apparent that power rotation of theshaft IS and its impeller assembly with the rods ifi'i of the latterpenetrating the body and intersecting the surface of a pulp chargewithin the bowl w will function to whip and agitate the pulp charge andto entrain air from above the charge surface along and iinmediatelybehind the moving rods ifi for dissemination as bubbles within andthroughout the agitated charge and for jet-like delivery from the rodfree ends at appropriate sp-eeds of rod translation.

` Apparatus characterized by impellers of the type shown in my earlierPatent No. 2,577,802, and hereinabove described has successfullyoperated to effectively agitate and to thoroughly and satisfactorilyaerate pulps of Various natures and consistencies for selective frothfiotation and for conditioning thereof, but factors pertinent to v'pulpreoirculation, to the development of circulatory currents Within thepulp, to scourng of the sediments from the cell bottoni, to maintenanceof a quiescent zone adjacent the froth bed, to the depth and location ofthe impeller Vortex, and to regulation of the induced air volume, aresignificant to the Operating eflicency of the particular impellerassembly shown and desoribed and give practical occasion for the furtherimprovernents of the present invention.

Primary to the organization and operation of the featurescharacteriz-ing the present invention, a hollow, frusto-conical shroudil is provided in a size and form to spacedly engage about and to housethe major length of the impeller assembly and the orbit of impeller rodIll revolution. As associated with the apparatus according to Figures1-4, inclusive, of the drawings, the shroud is provided with a coaxial,fiXedly-related, tubular neci Si extending from its lesser end fortelescopic engagement With and about the lower end of the sleeve 19 in atight frictional fit on, or other attachment to, the latter effective tomount the shroud 353 on and for altitudinal adjustment with said sl'eevein coaxial relation with the shaft E3 and associated impeller assemblyand in a doWnwardly-fiaring extension through the surface of the pulpcharge within the bowl and into the body of the pulp charge such as willposition the lower open end of the shroud somewhat above the planecommon to the lower or free ends of the rods l'l and dispose the shroudconical Wall in clearing relation about and outwardly from the impellerassembly rods Ill and their operative orbit, thus to permit freerotation of the impeller assembly interioriy of the shroud. Since theshroud 3B and its necl 3! fully house and enclose the impeller assemblyelements extending above the surface of the pulp charge in the bowl, itis clear that rotation of the impeller assembly as so housed will beineffectual to establish induction of air within and through the pulpcharge unless provision is made for supply of air, or analogous gases,to said necl: and the shroud lesser end, for which purpose a suitable owline 32 equipped with a valve 33 leads from atmosphere, or from a supplyof desred particular gas, to and opens at its delivery end through then-eck iii. Thus, when the impeller assembly is rotating interiorly ofthe shroud (it, the amount of air, or other gas, consequently introducedand disseminated Within the pulp charge may be controlled and regulatedby means of valve 33 adjustment and the position of the Vortex in thepulp surface incident to such impeller assembly rotation may becorrespondingly lowered or elevated within the shroud relative to thenormal pulp level in reaction to such valve manipulation.

Fixed to and outstanding laterally from and about the lower end of theshroud 313, a series of like, flat vanes 34 is arranged in a uniformangular spacing of the individual vane elements to dispose the latter asfixed bafiies within and substantially across the space between theshroud lower end and the adjacent bowl Wall. The vanes 35 areapproximately rectangular in plan, are similarly fixed at theircorresponding inner margins to the shroud lower end in a generallyradial projection therewith so as to position their outer marginssubstantially parallel with the bowl side wall, extend vertically acrossthe plane of the shroud open lower end to dispose their parallel upperand lower margins respectively above and below said plane and toposition their said lower margins adjacent and in clearing relationabove the floor of the bowl and in a common plane below that of theimpeller rod [4 free ends, and are preferably, though not necessarily,similarly inclined to the Vertical, substantially as shown. It is thefunction of the vanes 34 to modify and direct pulp currents andagitations developed by impeller assembly rotation in a manner and to adegree susceptible of regulation through Variation in the numberrelativesize, particular disposition, and inclination of the said vanes in agiven installation, the vane arrangement illustrated being obviouslyeffective upon impellergenerated pulp outfiow from the shroud lower endto interrupt and inhibit the development of pulp currents tending toswirl With the impeller circularly of the bowl, to direct pulp currentsagainst and with scourng effect upon the bowl floor, to stimulate pulpagitation through the generation of uprise currents along the bowl Wallsand between the vanes, and to thoroughly commingle the agitated pulpwith air or gas bubbles introduced along and delivered from the freeends of the rods Ill. Enhancing the pulp-agitating andbubble'-disseminating'A effect of the vanes 34, holes may beformed inand through said vanes in any number, particularV size, and patterndeemed to' be appropriate in a givenpractical application of/theapparatus, andV interruption and deflection of' radially-directed pulpcurrents may be effectively had, whendesired, through the provision ofan annularband 36, of appropriate width,- engaging and fixed to theouter margins of the vanes 34.

For maintenance of a pulp charge interiorly of the shroud 3d lowerportion subject to action of the 'impeller assembly and to accommodatecirculation and'recirculation of the pulpthrough the' influence-of theimpeller, the length'of said shroud is' interrupted'well below thenormal pulp level of lthe cell, and preferably a short distance abovethe upper margins of the vanes 34, by-an annular throat 31 ofoperatively-suitable"width axially of the shroud which extends entirelyabout the shroud in an orbit perpendicular" to the shroud axis andclivides said-shroud into an upper portion carried by the neck 3i and aseparate, lower shirt portion attached to and supported from said upperportion by suitable means, such as struts 38 bridging said throat 31 inangularly-spaced relation and fixedly end-engaged with the separatedshroud portions, the upper end of the shroud lower shirt portionexpediently being formed as a radialy and outwau'dlyl directed annularfiange 3i effective to stiffen the tubular shroud skirt and to directinfiow of pulp through the throat 31. With the impeller and shroudarrangement shown and described, rotation of the impeller assemblyoperates to exhaust pulp and intermingled air bub-bles from the shroudinterior through the open lower end of the shroud for agitationanduprise within the cell under the influence and direction of the vanesi'and band 36', the material so exhausted from the` shroudv interiorbeing continuously replaced by` infiow of pulp` through the throat 3'iwith consequent most thorough recirculation of the pulp andagitationthereof in intimate and` repetitious exposure to the air or gas bubblesgenerated within the pulp byV the impeller action.

In accordance with the principles of froth flotation, the'air or gasbubbles generated within the cell rise through the'pulp charge'withthepulp part'icles to which they have become attached and colle'ct onand above the pulp level of the cell as a froth `ced removable over thelip H'for segregation of the material levitated thereby, such uprise ofthe bubbles and the'efiicient collection thereof in and as a froth bedon the pulpsurface being facilitated with advantage-of separatory,7efiiciency through damping out of turbulence and eddy currents'in theupper levelsiof the pulp charge and the consequent provision of aqui'escent pulp zone underlying the froth'bed. For the purposes and todevelop the effects just above noted, it .ispractical and'convenient-lto provide a diffusing bafile dil'zion and about the shroud 30 above thethroat 3 `l"in a Vgenerally horizontal disposition across thespace-between the shroud and the cell: side wall,

saidfbaffle llpreferably being in the form of a somewhat fiattenedfrustoconicalplate conform'ed in-plan with the bowl l and of a size toslidably engage within said bowl, an opening centrally'and through thelesser end of said plate sized andv conformed to embracethe shroucl 30upper portionand to marginally engage said shroud portion immeoliatelyVabovethe throat 3'1 for positioned supportof the battle thereon, holes4-I intersectingl thebafl'ie conical' area'in such size, number, andpattern as willV adequatelyaccommodatel uprse3 of. air and gas'bubbl'estherethroug'h, andanupturned lip;4Zfperipherallyvofthe bafile-platefacilitative of baiile plate introduction'within, .and ad- J'ustment'.thereof altitudinally of,V the bowl Ill.

Withthe baiiie-li positioned as shown and described, the turbulence andeddy: currents generated byfimpeller assembly rotation are largelyconfined-to thervlower area: of 'the pulp=charge below-said bafiieandldeflected away from' disturbing effectuponthepulp chargearea` abovethe baflle'.

the air or gas'ibubbles approaching. and imping-ingagainstV the baiflepassingv through the holes M' thereofV by Virtue 'of their tendencytouprise vertically through the pulpv andl completing such uprise tothepulp surface through the relatively quiet Aupper areaiof the-pulp:charge with a minimunrof collapse andloss of their partiole charges;

thecomparatively undisturbed sur-face :of the pulp charge* facilitatingdevelopment of the desired.

froth bed' in fioatingrelation therewith.

In a structural arrangement and operativeor'- ganization analogous' tothat hereinabove described, the improvementsofrz the-present inventionare-'shown inlF'igures 7-10; inclusive, asassociated -for practical'usein and with a cell'adapted to accomplishieither froth'fiotative orconditioning treatment of 'a pulp. In the-views last above noted, thece1l2 iii! is-shown as rectangular inl plan, asformed with a-fioorinwardlyl and down- Wardly-sloped fromf each'sicle of 'the cell to ahorizontal iioor area centrally and longitudinally of the cell,andasassoci'ated for 'continuous flow operation with'a pulp feedbox'f43\ arranged for input z of pulp'to theV cellat and to oneend'ofthecell floor centralarea-andfor delivery of' treatedpulpthroughiahoodedioutfiow orifice M to a -succeeding cell IG,all'in-accord'ance with known and conventional' practice.

top wli'ereon the'tubular sleeve i9'ispositioned and supportedfwithitslaxis verticaland centrally offthe cellto dispose the shaftv l3 withits associated impeller assemblyof'rods) 14' and-collar i d in forrotatioirrelative to the cell'inl theimanner and for the purposes ofpulp agitation and air induction'previouslx'r described. The motor isfadjustably carried by the bridge 45 with its shaft Vertical so-thatthepulleys 22 and 23 may engage the belt''tfor completion of a power driveto the shaft iandimpeller assembly as previously set forth. Structurallyand'functionally analogousto'the'shroud 3d, a frusto-conical shroud 351'cornprised of upper and lower portions separated by an annular1 throat31' is supplied with fixedly-re-- lated'stem members 46 engaging itsexterior surface and bridging'the throat 37' to interconnect theotherwise separate shroud 36 portions, and extensions of said members 46beyond the lesser end ofthe'shroud are arranged to parallel the shroudaxis and threaded for a'distance adjacent their free ends, so that whensaid member extensions-are engaged through holes in elements of.

the'bridge 45 supportingthe sleeve l'and with nuts'adjusted tobearagainst said'bridge elements.

pose the'collar l5 and rod l4` upper endsabove its lesser end' plane andto establishprojection ofithe ro'd-l 4 free ends below its greater endplane,

the saidlesser and greater endsV of the shroud'? The cell'| Hi! isfurnished with a-rigid bridge 45fixedly' spanning its open'v beingpreferably stiifened and reinforced by means of annular fianges 39'outstanding radially therefrom and the shroud lesser end preferablybeing formed as an axially-short cylindrical band Ill upstanding incoaxial relation therefrom. At its lower end the shroud 30' carriesfixedlyrelated vanes 34', each preferably intersected by a plurality ofholes 35', in a radially-outstanding, angularly-spaced, preferablyinclined arrangement structurally and functionally the same as that ofthe vanes 34 of the embodiment rst described, and outer ends of the saidvanes 34' close against and are encircled by an annular band 36' whichmay be operatively associated with and for altitudinal adjustmentrelative to the vanes by means of slotted ears 48 fixed to and extendinginwardly from the band inner surface to conformably overlie certain ofthe vane outer ends in clampable association with bolts 49 engagedthrough the said vane ends and the slots of said ears.

When utilized for froth flotation purposes, the organization representedin Figures 7, 8, 9 and 10 operates to agtate, aerate, and recirculatethe pulp in an obvious manner closely similar, except for regulation ofair infiow to the impeller, to that charactcrizing operation of thefirst-described embodiment of the improvements. For such froth flotativeoperation of the apparatus,

the level L of the cell pulp charge is established,

through altitudinal adjustment of the shroud 30' or through regulationof pulp flow to and through the cell, or both, at a plane below that ofthe band 47 upper end, thereby to inhibt inflow of pulp to the shroudthrough its open upper end and to dispose said band M as a bafiieupstanding through the froth bed to dam the latter` away fromentrainment within the pulp body, thus constituting the open throat 37'as the means accommodating inflow of pulp from the cell and to theshroud interior as the impeller acts to exhaust pulp from and throughthe lower end of the shroud, whereby to effectively recirculate the pulpin the lower area of the cell and to minimize the development of eddiesand currents within the progressively more quiet pulp zones above saidthroat.

For thorough and repetitious agitation of the entire pulp charge, as inthe conditioning of ore pulps in the presence of reagents, and the like,the apparatus represented in Figures 7, 8, 9 and 10 may be efciently andadvantageously utilized simply by closing the throat 31' of the shroud30' and adjusting the level of the cell pulp charge, through regulationof pulp flow to and through the cell or by varying the altitudinaldisposition of the shroud, to a relation with the shroud open upper endindicated at L" such as will submerge the shroud wholly within the pulpcharge and establish a continuous feed of pulp to the shroud interiorthrough the open collar 41 when and as the impeller is Operating.Various expedients may be availed of for selectively closing the shroudthroat 31", a convenient arrangement for such purpose being illustratedas comprising segmental skirt plates B adapted to close over the throatareas between the stem members 46 in engagernent with positioning andsupporting means, such as hooks 55 and latch studs 52, carried by theshroud.

Obviously, the balfle Lit may be utilized with the shroud 3i`i' in themanner and for the purposes to which it is applied in association withthe shroud 30, the shroud 36 may be open to atmosphere at its lesser endand provided with closures for its throat 31, whereby to adapt it foruse in the conditioning of the pulp, and the shoud 3B' may be providedwith a chamber at its upper end closed to atmosphere and furnished witha valved inlet, in the manner and for the purposes characterizing thelike means associated with the shroud 3%, all such relationships andreorganizations of the elements shown and described being clearly Withinthe manifest scope and contemplation of the invention.

Since changes, variations, and modifications in the form, construction,and arrangement of the elements shown and described may be had withoutdeparting from the spirit of my invention, I wish to be understood asbeing limited solely by the scope of the appended claims, rather than byany details of the illustrative showing and foregoing description.

I claim as my invention:

l. The combination with an open-top cell adapted to contain ore pulp anda verticallyaxised, frusto-conical impeller assembly ofangularly-spaced, divergent rods rotatable about its axis in agitatingand aerating relation with the cell pulp charge with its lesser enduppermost, of a frusto-conical shroud non-rotatably fixed coaxially withand spacedly about the major length of said impeller with the shroudlower end upwardly adjacent the lower end of the imfpeller, vanesfixedly outstanding radially from and in angularly-spaced relation aboutthe lower end of said shroud with their outer ends inwardly clearing thecell walls and their lower margins in a plane above the cell floor andbelow the lower end of the impeller assembly, and a throatcircumferentially interrupting said shroud above said vanes for thecirculation of pulp therethrough.

2. The combination with an open-top cell adapted to contain ore pulp anda verticallyaxised, frusto-conical impeller assembly ofangularly-spaced, divergent rods rotatable about its axis in agitatingand aerating relation with the cell pulp charge with its lesser enduppermost, of a frusto-conical shroud non-rotatably and inangularly-spaced relation about the lower end of said shroud with theirouter ends inwardly clearing the Cell walls and their lower margins in aplane above the cell fioor and below the lower end of the impellerassembly, a throat circum- -ferentially interrupting said shroud abovesaid vanes for the circulation of pulp therethrough, a neck extension ofthe shroud upper end defining a Chamber closed to atmosphere, and avalve- Controlled inlet to said chamber above the pulp charge level.

3. The combination with an open-top cell adapted to contain ore pulp anda verticallyaxised, frusto-conical impeller assembly ofangularly-spaced, divergent rods rotatable about its aXis in agitatingand aerating relation with the cell pulp charge with its lesser enduppermost, of a frusto-conical shroud non-rotatably fixed coaxially withand spacedly about the major length of said impeller with the shroudlower end upwardly adjacent the lower end of the impeller, vanes fixedlyoutstanding radially from and in angularly-spaced relation about thelower end of the shroud with their outer ends inwardly clearing the cellwalls and their lower margins in a plane above the cell floor and belowthe lower end of the impeller assembly,` a throat circumferentiallyinterrupting said shroud above said vanes for the circulation of pulp.therethrough, and a baflie engaged with and exteriorly about said shroudimmediately above said throat in spacedly-overhanging relation with saidvanes.

4. The combination with an open-top cell adapted to contain ore pulp anda verticallyaxised, frusto-con'ical impeller assembly ofangularly-spaced, divergent rods rotatable about its axis in agitatingand aerating relation with the cell pulp charge with its lesser enduppermost, of a frusto-conical shroud non-rotatably fixed coaxially withand spacedly about the major length of said impeller with the shroudlower end upwardly adjacentthe lower end of the impeller, vanes fixedlyoutstanding radially from and in angularly-spaced relation about' thelower end of said shroud with their outer ends inwardly clearing thecell walls and their lower margins in a plane above the cell floor andbelow the lower end of the impeller assembly, a throat circumferentiallyinterrupting said shroud above said vanes for the circulation of pulptherethrough, a neck extension of the shroud upper end defining achamber closed to atmosphere, a valve-controlled inlet to said chamberabove the pulp charge level, and a baffle engaged with an exteriorlyabout said shroud immediately above said throat in spacedly-overhangingrelation with said vanes.

5. The combination with an open-top cell adapted to contain ore pulp anda verticallyaxised, frusto-conical impeller assembly ofangularly-spaced, divergent rods rotatable about its axis in agitatingand aerating relation with the cell pulp charge with its lesser enduppermost, of a frusto-conical shroud non-rotatably fixed and mountedfor altitudinal adjustment e coaxially with and spacedly about the majorlength of said impeller with the shroud lower end at all times upwardlyadjacent the lower end of the impeller, vanes fixedly outstandingradially from and in angularly-spaced relation about the lower end ofsaid shroud with their outer ends inwardly clearing the cell walls andtheir lower margins in a plane above the cell floor and below the lowerend of the impeller assembly, a throat circumferentially interruptingsaid shroud above said vanes for the circulation of pulp therethrough,an annular collar concentrically upstanding from the shroud lesser endand altitudinally adjustable with the shroud between extension above andsubmergence below the pulp charge level, and means for selectivelyclosing said throat.

6. In apparatus of the character described having an open-top celladapted to contain ore pulp and a vertically-axised impeller assembly ofangu1arly-spaced, divergent rods rotatable about its axis in agitatingand aerating relation with the cell pulp charge with its lesser enduppermost, a frusto-conical shroud non-rotatably fixed coaxially withand spacedly about the major length of said impeller with the shroudlower end upwardly adjacent the lower end of the impeller, vanes fixedlyoutstanding from and in angularly-spaced relation about the lower end ofthe shroud with their outer ends inwardly clearing the cell walls andtheir lower margins in a plane above the cell fioor and below the lowerend of the impeller assembly, and a throat circumferentiallyinterrupting said shroud above 10 the vanes to. provide a pulprecirculation passage to the shroud interior.

7. In apparatus of the character described having an open-top celladapted to contain ore pulp and a vertically-axised impeller assernblyof angularly-spaced, divergent rods rotatable about its axis inagitating and aerating relation with the cell pulp charge with itslesser' end uppermost, a frusto-con-ical shroud non-rotatably fixeddefining a Chamber closed to atmosphere, and a valve-Controlled inletcommunicating with said chamber above the cell pulp charge level.

8. In apparatus of .the character described having an open-top celladapted to contain ore pulp and a vertically-axised impeller assembly'of an'- gularly-spaced, divergent rods rotatable about its axis inagitating and aerating relation with the cell pulp charge with itslesser end uppermost, a frusto-conical shroud non-rotatably fixedcoaxially with and spacedly about the major length of said impeller withthe shroud lower end upwardly adjacent the lower end of the impeller,vanes fixedly outstanding from and in angularlyspaced relation about thelower end of the shroud with their outer ends inwardly clearing the cellwalls and their lower margins in a plane above the cell fioor and belowthe lower end of the impeller assembly, a throat circumferentiallyintersecting said shroud above the vanes to provide a pulp recirculationpassage to the shroud interior, and a baifle engaging with andexteriorly about said shroud immediately above said throat inspacedly-overhanging relation with said vanes.

9. In apparatus of the character described having an open-top celladapted to contain ore pulp and a vertically-axised impeller assembly ofangularly-spaced, divergent rods rotatable about its axis in agitatingand aerating relation with the cell pulp charge with its lesser enduppermost, a frust-o-conical shroud non-rotatably fixed coaxially withand spaced about the major length of said impeller with the shroud lowerend upwardly adjacent the lower end of the impeller, vanes fixedlyoutstanding from and in angularlyspaced relation about the lower end ofthe shroud with their outer ends inwardly clearing the cell walls andtheir lower margins in a plane above the cell fioor and below the lowerend of the impeller assembly, a throat circumferentially intersectingsaid shroud above the vanes to provide a pulp recirculation passage tothe shroud interior, a bafile engaging with and exteriorly about saidshroud immediately above said throat in spacedly-overhanging relationwith said vanes, and apertures extensively interrupting said baii'le andsaid vanes for pulpcirculation therethrough.

10. In apparatus of the Character described having an open-top celladapted to contain ore pulp and a vertically-axised impeller assembly ofangularly-spaced, divergent rods rotatable about its axis in agitatingand aerating relation with the cell pulp charge with its lesser enduppermost, a frusto-conical shroud non-rotatably fixed coaxially withand spacedly about the major length of said impeller with the shroudlower end upwardly adjacent the lower end of the impeller, vanes xedlyoutstanding from and in angularly-spaced relation about the lower end ofthe shroud with their outer ends inwardly clearing the cell walls andtheir lower margins in a plane above the cell fioor and below the lowerend of the impeller assembly, a throat circumferentially intersectingsaid shroud above the vanes to provide a pulp recirculation passage tothe shroud interior, a neck extension of the shroud upper end defining aChamber closed to atmosphere, a valve-Controlled inlet communicatingwith said Chamber above the cell pulp charge level, and a baflleengaging with and exteriorly about said shroud immediately above saidthroat in spacedly-overhanging relation with said vanes.

11. In apparatus of the character described having an open-top celladapted to contain ore pulp and a vertically-axised impeller assembly ofangularly-spaced, divergent rods rotatable about its axis in agitatingand aerating relation with the cell pulp charge with its lesser enduppermost, a frusto-conical shroud non-rotatably fixed coaxially withand spacedly about the major length of said impeller with the shroudlower end upwardly adjacent the lower end of the impeller, vanes fixedlyoutstanding from and in angularly-spaced relation about the lower end ofthe shroud with their outer ends inwardly clearing the cell walls andtheir lower margins in a pl'ane above the cell fioor and below the lowerend of the impeller assembly, and an annular band coaxial with saidshroud embracing and engaging the outer ends of said vanes in clearingrelation with and above the cell floor.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,597,316 Hutchings Aug. 24, 1926 1,796,2'78 Bakewell Mar. 17,1931 1,976,956 MacLean Oct. 16, 1934 2,031,590 Daman Feb. 25, 19362,190,852 Tucker Feb. 20, 1940 2,433,592 Booth Dec. 20, 1947 2,578,805Johnson Dec. 18, 1951 FOREIGN PATENTS Number Country Date 15,292 GreatBritain June 30, 1911

